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Summary: Ctors | Methods | Inherited Methods

# StringBuilder

`public final class StringBuilder`
`extends Object` `implements Appendable, CharSequence, Serializable`

java.lang.Object
↳ | java.lang.StringBuilder

A mutable sequence of characters. This class provides an API compatible with `StringBuffer`, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for `StringBuffer` in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to `StringBuffer` as it will be faster under most implementations.

The principal operations on a `StringBuilder` are the `append` and `insert` methods, which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends or inserts the characters of that string to the string builder. The `append` method always adds these characters at the end of the builder; the `insert` method adds the characters at a specified point.

For example, if `z` refers to a string builder object whose current contents are "`start`", then the method call `z.append("le")` would cause the string builder to contain "`startle`", whereas `z.insert(4, "le")` would alter the string builder to contain "`starlet`".

In general, if sb refers to an instance of a `StringBuilder`, then `sb.append(x)` has the same effect as `sb.insert(sb.length(), x)`.

Every string builder has a capacity. As long as the length of the character sequence contained in the string builder does not exceed the capacity, it is not necessary to allocate a new internal buffer. If the internal buffer overflows, it is automatically made larger.

Instances of `StringBuilder` are not safe for use by multiple threads. If such synchronization is required then it is recommended that `StringBuffer` be used.

Unless otherwise noted, passing a `null` argument to a constructor or method in this class will cause a `NullPointerException` to be thrown.

See also:

- `StringBuffer`
- `String`

## Summary

### Public constructors
`StringBuilder()` Constructs a string builder with no characters in it and an initial capacity of 16 characters.
`StringBuilder(int capacity)` Constructs a string builder with no characters in it and an initial capacity specified by the `capacity` argument.
`StringBuilder(String str)` Constructs a string builder initialized to the contents of the specified string.
`StringBuilder(CharSequence seq)` Constructs a string builder that contains the same characters as the specified `CharSequence`.

### Public methods
`StringBuilder` | `append(boolean b)`
`StringBuilder` | `append(long lng)`
`StringBuilder` | `append(char c)` Appends the specified character to this `Appendable`.
`StringBuilder` | `append(Object obj)`
`StringBuilder` | `append(char[] str, int offset, int len)`
`StringBuilder` | `append(double d)`
`StringBuilder` | `append(char[] str)`
`StringBuilder` | `append(String str)`
`StringBuilder` | `append(StringBuffer sb)` Appends the specified `StringBuffer` to this sequence.
`StringBuilder` | `append(float f)`
`StringBuilder` | `append(int i)`
`StringBuilder` | `append(CharSequence s, int start, int end)` Appends a subsequence of the specified character sequence to this `Appendable`.
`StringBuilder` | `append(CharSequence s)` Appends the specified character sequence to this `Appendable`.
`StringBuilder` | `appendCodePoint(int codePoint)`
`int` | `capacity()` Returns the current capacity.
`char` | `charAt(int index)` Returns the `char` value in this sequence at the specified index.
`int` | `codePointAt(int index)` Returns the character (Unicode code point) at the specified index.
`int` | `codePointBefore(int index)` Returns the character (Unicode code point) before the specified index.
`int` | `codePointCount(int beginIndex, int endIndex)` Returns the number of Unicode code points in the specified text range of this sequence.
`StringBuilder` | `delete(int start, int end)`
`StringBuilder` | `deleteCharAt(int index)`
`void` | `ensureCapacity(int minimumCapacity)` Ensures that the capacity is at least equal to the specified minimum.
`void` | `getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)` Characters are copied from this sequence into the destination character array `dst`.
`int` | `indexOf(String str)`
`int` | `indexOf(String str, int fromIndex)`
`StringBuilder` | `insert(int offset, char[] str)`
`StringBuilder` | `insert(int offset, float f)`
`StringBuilder` | `insert(int dstOffset, CharSequence s)`
`StringBuilder` | `insert(int offset, char c)`
`StringBuilder` | `insert(int offset, long l)`
`StringBuilder` | `insert(int index, char[] str, int offset, int len)`
`StringBuilder` | `insert(int offset, int i)`
`StringBuilder` | `insert(int offset, String str)`
`StringBuilder` | `insert(int offset, double d)`
`StringBuilder` | `insert(int dstOffset, CharSequence s, int start, int end)`
`StringBuilder` | `insert(int offset, Object obj)`
`StringBuilder` | `insert(int offset, boolean b)`
`int` | `lastIndexOf(String str, int fromIndex)`
`int` | `lastIndexOf(String str)`
`int` | `length()` Returns the length (character count).
`int` | `offsetByCodePoints(int index, int codePointOffset)` Returns the index within this sequence that is offset from the given `index` by `codePointOffset` code points.
`StringBuilder` | `replace(int start, int end, String str)`
`StringBuilder` | `reverse()`
`void` | `setCharAt(int index, char ch)` The character at the specified index is set to `ch`.
`void` | `setLength(int newLength)` Sets the length of the character sequence.
`CharSequence` | `subSequence(int start, int end)` Returns a new character sequence that is a subsequence of this sequence.
`String` | `substring(int start, int end)` Returns a new `String` that contains a subsequence of characters currently contained in this sequence.
`String` | `substring(int start)` Returns a new `String` that contains a subsequence of characters currently contained in this character sequence.
`String` | `toString()` Returns a string representation of the object.
`void` | `trimToSize()` Attempts to reduce storage used for the character sequence.

### Inherited methods
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.
From interface `java.lang.Appendable`
`abstract Appendable` | `append(char c)` Appends the specified character to this `Appendable`.
`abstract Appendable` | `append(CharSequence csq, int start, int end)` Appends a subsequence of the specified character sequence to this `Appendable`.
`abstract Appendable` | `append(CharSequence csq)` Appends the specified character sequence to this `Appendable`.
From interface `java.lang.CharSequence`
`abstract char` | `charAt(int index)` Returns the `char` value at the specified index.
`default IntStream` | `chars()` Returns a stream of `int` zero-extending the `char` values from this sequence.
`default IntStream` | `codePoints()` Returns a stream of code point values from this sequence.
`abstract int` | `length()` Returns the length of this character sequence.
`abstract CharSequence` | `subSequence(int start, int end)` Returns a `CharSequence` that is a subsequence of this sequence.
`abstract String` | `toString()` Returns a string containing the characters in this sequence in the same order as this sequence.

## Public constructors

### StringBuilder

    public StringBuilder ()

Constructs a string builder with no characters in it and an initial capacity of 16 characters.

### StringBuilder

    public StringBuilder (int capacity)

Constructs a string builder with no characters in it and an initial capacity specified by the `capacity` argument.

Parameters
`capacity` | `int`: the initial capacity.

Throws
`NegativeArraySizeException` | if the `capacity` argument is less than `0`.

### StringBuilder

    public StringBuilder (String str)

Constructs a string builder initialized to the contents of the specified string. The initial capacity of the string builder is `16` plus the length of the string argument.

Parameters
`str` | `String`: the initial contents of the buffer.

### StringBuilder

    public StringBuilder (CharSequence seq)

Constructs a string builder that contains the same characters as the specified `CharSequence`. The initial capacity of the string builder is `16` plus the length of the `CharSequence` argument.

Parameters
`seq` | `CharSequence`: the sequence to copy.

## Public methods

### append

    public StringBuilder append (boolean b)

Parameters
`b` | `boolean`

Returns
`StringBuilder` |

### append

    public StringBuilder append (long lng)

Parameters
`lng` | `long`

Returns
`StringBuilder` |

### append

    public StringBuilder append (char c)

Appends the specified character to this `Appendable`.

Parameters
`c` | `char`: The character to append

Returns
`StringBuilder` | A reference to this `Appendable`

### append

    public StringBuilder append (Object obj)

Parameters
`obj` | `Object`

Returns
`StringBuilder` |

### append

    public StringBuilder append (char[] str,
                    int offset,
                    int len)

Parameters
`str` | `char`
`offset` | `int`
`len` | `int`

Returns
`StringBuilder` |

Throws
`IndexOutOfBoundsException` |

### append

    public StringBuilder append (double d)

Parameters
`d` | `double`

Returns
`StringBuilder` |

### append

    public StringBuilder append (char[] str)

Parameters
`str` | `char`

Returns
`StringBuilder` |

### append

    public StringBuilder append (String str)

Parameters
`str` | `String`

Returns
`StringBuilder` |

### append

    public StringBuilder append (StringBuffer sb)

Appends the specified `StringBuffer` to this sequence.

The characters of the `StringBuffer` argument are appended, in order, to this sequence, increasing the length of this sequence by the length of the argument. If `sb` is `null`, then the four characters `"null"` are appended to this sequence.

Let n be the length of this character sequence just prior to execution of the `append` method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument `sb`.

Parameters
`sb` | `StringBuffer`: the `StringBuffer` to append.

Returns
`StringBuilder` | a reference to this object.

### append

    public StringBuilder append (float f)

Parameters
`f` | `float`

Returns
`StringBuilder` |

### append

    public StringBuilder append (int i)

Parameters
`i` | `int`

Returns
`StringBuilder` |

### append

    public StringBuilder append (CharSequence s,
                    int start,
                    int end)

Appends a subsequence of the specified character sequence to this `Appendable`.

An invocation of this method of the form `out.append(csq, start, end)` when `csq` is not `null`, behaves in exactly the same way as the invocation

         out.append(csq.subSequence(start, end))

Parameters
`s` | `CharSequence`: The character sequence from which a subsequence will be appended. If `csq` is `null`, then characters will be appended as if `csq` contained the four characters `"null"`.
`start` | `int`: The index of the first character in the subsequence
`end` | `int`: The index of the character following the last character in the subsequence

Returns
`StringBuilder` | A reference to this `Appendable`

Throws
`IndexOutOfBoundsException` |

### append

    public StringBuilder append (CharSequence s)

Appends the specified character sequence to this `Appendable`.

Depending on which class implements the character sequence `csq`, the entire sequence may not be appended. For instance, if `csq` is a `CharBuffer` then the subsequence to append is defined by the buffer's position and limit.

Parameters
`s` | `CharSequence`: The character sequence to append. If `csq` is `null`, then the four characters `"null"` are appended to this Appendable.

Returns
`StringBuilder` | A reference to this `Appendable`

### appendCodePoint

    public StringBuilder appendCodePoint (int codePoint)

Parameters
`codePoint` | `int`

Returns
`StringBuilder` |

### capacity

    public int capacity ()

Returns the current capacity. The capacity is the amount of storage available for newly inserted characters, beyond which an allocation will occur.

Returns
`int` | the current capacity

### charAt

    public char charAt (int index)

Returns the `char` value in this sequence at the specified index. The first `char` value is at index `0`, the next at index `1`, and so on, as in array indexing.

The index argument must be greater than or equal to `0`, and less than the length of this sequence.

If the `char` value specified by the index is a surrogate, the surrogate value is returned.

Parameters
`index` | `int`: the index of the desired `char` value.

Returns
`char` | the `char` value at the specified index.

Throws
`IndexOutOfBoundsException` | if `index` is negative or greater than or equal to `length()`.

### codePointAt

    public int codePointAt (int index)

Returns the character (Unicode code point) at the specified index. The index refers to `char` values (Unicode code units) and ranges from `0` to `length()``- 1`.

If the `char` value specified at the given index is in the high-surrogate range, the following index is less than the length of this sequence, and the `char` value at the following index is in the low-surrogate range, then the supplementary code point corresponding to this surrogate pair is returned. Otherwise, the `char` value at the given index is returned.

Parameters
`index` | `int`: the index to the `char` values

Returns
`int` | the code point value of the character at the `index`

Throws
`IndexOutOfBoundsException` | if the `index` argument is negative or not less than the length of this sequence.

### codePointBefore

    public int codePointBefore (int index)

Returns the character (Unicode code point) before the specified index. The index refers to `char` values (Unicode code units) and ranges from `1` to `length()`.

If the `char` value at `(index - 1)` is in the low-surrogate range, `(index - 2)` is not negative, and the `char` value at `(index - 2)` is in the high-surrogate range, then the supplementary code point value of the surrogate pair is returned. If the `char` value at `index - 1` is an unpaired low-surrogate or a high-surrogate, the surrogate value is returned.

Parameters
`index` | `int`: the index following the code point that should be returned

Returns
`int` | the Unicode code point value before the given index.

Throws
`IndexOutOfBoundsException` | if the `index` argument is less than 1 or greater than the length of this sequence.

### codePointCount

    public int codePointCount (int beginIndex,
                    int endIndex)

Returns the number of Unicode code points in the specified text range of this sequence. The text range begins at the specified `beginIndex` and extends to the `char` at index `endIndex - 1`. Thus the length (in `char`s) of the text range is `endIndex-beginIndex`. Unpaired surrogates within this sequence count as one code point each.

Parameters
`beginIndex` | `int`: the index to the first `char` of the text range.
`endIndex` | `int`: the index after the last `char` of the text range.

Returns
`int` | the number of Unicode code points in the specified text range

Throws
`IndexOutOfBoundsException` | if the `beginIndex` is negative, or `endIndex` is larger than the length of this sequence, or `beginIndex` is larger than `endIndex`.

### delete

    public StringBuilder delete (int start,
                    int end)

Parameters
`start` | `int`
`end` | `int`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### deleteCharAt

    public StringBuilder deleteCharAt (int index)

Parameters
`index` | `int`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### ensureCapacity

    public void ensureCapacity (int minimumCapacity)

Ensures that the capacity is at least equal to the specified minimum. If the current capacity is less than the argument, then a new internal array is allocated with greater capacity. The new capacity is the larger of:

- The `minimumCapacity` argument.
- Twice the old capacity, plus `2`.

If the `minimumCapacity` argument is nonpositive, this method takes no action and simply returns. Note that subsequent operations on this object can reduce the actual capacity below that requested here.

Parameters
`minimumCapacity` | `int`: the minimum desired capacity.

### getChars

    public void getChars (int srcBegin,
                    int srcEnd,
                    char[] dst,
                    int dstBegin)

Characters are copied from this sequence into the destination character array `dst`. The first character to be copied is at index `srcBegin`; the last character to be copied is at index `srcEnd-1`. The total number of characters to be copied is `srcEnd-srcBegin`. The characters are copied into the subarray of `dst` starting at index `dstBegin` and ending at index:

    dstbegin + (srcEnd-srcBegin) - 1

Parameters
`srcBegin` | `int`: start copying at this offset.
`srcEnd` | `int`: stop copying at this offset.
`dst` | `char`: the array to copy the data into.
`dstBegin` | `int`: offset into `dst`.

Throws
`IndexOutOfBoundsException` | if any of the following is true: `srcBegin` is negative `dstBegin` is negative the `srcBegin` argument is greater than the `srcEnd` argument. `srcEnd` is greater than `this.length()`. `dstBegin+srcEnd-srcBegin` is greater than `dst.length`

### indexOf

    public int indexOf (String str)

Parameters
`str` | `String`

Returns
`int` |

### indexOf

    public int indexOf (String str,
                    int fromIndex)

Parameters
`str` | `String`
`fromIndex` | `int`

Returns
`int` |

### insert

    public StringBuilder insert (int offset,
                    char[] str)

Parameters
`offset` | `int`
`str` | `char`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    float f)

Parameters
`offset` | `int`
`f` | `float`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int dstOffset,
                    CharSequence s)

Parameters
`dstOffset` | `int`
`s` | `CharSequence`

Returns
`StringBuilder` |

Throws
`IndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    char c)

Parameters
`offset` | `int`
`c` | `char`

Returns
`StringBuilder` |

Throws
`IndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    long l)

Parameters
`offset` | `int`
`l` | `long`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int index,
                    char[] str,
                    int offset,
                    int len)

Parameters
`index` | `int`
`str` | `char`
`offset` | `int`
`len` | `int`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    int i)

Parameters
`offset` | `int`
`i` | `int`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    String str)

Parameters
`offset` | `int`
`str` | `String`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    double d)

Parameters
`offset` | `int`
`d` | `double`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int dstOffset,
                    CharSequence s,
                    int start,
                    int end)

Parameters
`dstOffset` | `int`
`s` | `CharSequence`
`start` | `int`
`end` | `int`

Returns
`StringBuilder` |

Throws
`IndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    Object obj)

Parameters
`offset` | `int`
`obj` | `Object`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### insert

    public StringBuilder insert (int offset,
                    boolean b)

Parameters
`offset` | `int`
`b` | `boolean`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### lastIndexOf

    public int lastIndexOf (String str,
                    int fromIndex)

Parameters
`str` | `String`
`fromIndex` | `int`

Returns
`int` |

### lastIndexOf

    public int lastIndexOf (String str)

Parameters
`str` | `String`

Returns
`int` |

### length

    public int length ()

Returns the length (character count).

Returns
`int` | the length of the sequence of characters currently represented by this object

### offsetByCodePoints

    public int offsetByCodePoints (int index,
                    int codePointOffset)

Returns the index within this sequence that is offset from the given `index` by `codePointOffset` code points. Unpaired surrogates within the text range given by `index` and `codePointOffset` count as one code point each.

Parameters
`index` | `int`: the index to be offset
`codePointOffset` | `int`: the offset in code points

Returns
`int` | the index within this sequence

Throws
`IndexOutOfBoundsException` | if `index` is negative or larger then the length of this sequence, or if `codePointOffset` is positive and the subsequence starting with `index` has fewer than `codePointOffset` code points, or if `codePointOffset` is negative and the subsequence before `index` has fewer than the absolute value of `codePointOffset` code points.

### replace

    public StringBuilder replace (int start,
                    int end,
                    String str)

Parameters
`start` | `int`
`end` | `int`
`str` | `String`

Returns
`StringBuilder` |

Throws
`StringIndexOutOfBoundsException` |

### reverse

    public StringBuilder reverse ()

Returns
`StringBuilder` |

### setCharAt

    public void setCharAt (int index,
                    char ch)

The character at the specified index is set to `ch`. This sequence is altered to represent a new character sequence that is identical to the old character sequence, except that it contains the character `ch` at position `index`.

The index argument must be greater than or equal to `0`, and less than the length of this sequence.

Parameters
`index` | `int`: the index of the character to modify.
`ch` | `char`: the new character.

Throws
`IndexOutOfBoundsException` | if `index` is negative or greater than or equal to `length()`.

### setLength

    public void setLength (int newLength)

Sets the length of the character sequence. The sequence is changed to a new character sequence whose length is specified by the argument. For every nonnegative index k less than `newLength`, the character at index k in the new character sequence is the same as the character at index k in the old sequence if k is less than the length of the old character sequence; otherwise, it is the null character `'\u0000'`. In other words, if the `newLength` argument is less than the current length, the length is changed to the specified length.

If the `newLength` argument is greater than or equal to the current length, sufficient null characters (`'\u0000'`) are appended so that length becomes the `newLength` argument.

The `newLength` argument must be greater than or equal to `0`.

Parameters
`newLength` | `int`: the new length

Throws
`IndexOutOfBoundsException` | if the `newLength` argument is negative.

### subSequence

    public CharSequence subSequence (int start,
                    int end)

Returns a new character sequence that is a subsequence of this sequence.

An invocation of this method of the form

    sb.subSequence(begin,&nbsp;end)

behaves in exactly the same way as the invocation

    sb.substring(begin,&nbsp;end)

This method is provided so that this class can implement the `CharSequence` interface.

Parameters
`start` | `int`: the start index, inclusive.
`end` | `int`: the end index, exclusive.

Returns
`CharSequence` | the specified subsequence.

Throws
`IndexOutOfBoundsException` | if `start` or `end` are negative, if `end` is greater than `length()`, or if `start` is greater than `end`

### substring

    public String substring (int start,
                    int end)

Returns a new `String` that contains a subsequence of characters currently contained in this sequence. The substring begins at the specified `start` and extends to the character at index `end - 1`.

Parameters
`start` | `int`: The beginning index, inclusive.
`end` | `int`: The ending index, exclusive.

Returns
`String` | The new string.

Throws
`StringIndexOutOfBoundsException` | if `start` or `end` are negative or greater than `length()`, or `start` is greater than `end`.

### substring

    public String substring (int start)

Returns a new `String` that contains a subsequence of characters currently contained in this character sequence. The substring begins at the specified index and extends to the end of this sequence.

Parameters
`start` | `int`: The beginning index, inclusive.

Returns
`String` | The new string.

Throws
`StringIndexOutOfBoundsException` | if `start` is less than zero, or greater than the length of this object.

### toString

    public String toString ()

Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

>      getClass().getName() + '@' + Integer.toHexString(hashCode())

Returns
`String` | a string representation of the object.

### trimToSize

    public void trimToSize ()

Attempts to reduce storage used for the character sequence. If the buffer is larger than necessary to hold its current sequence of characters, then it may be resized to become more space efficient. Calling this method may, but is not required to, affect the value returned by a subsequent call to the `capacity()` method.

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